Testing compliance with occupational exposure limits (OELs) for airborne substances: the new revision of European Standard EN 689

Transcription

1 Testing compliance with occupational exposure limits (OELs) for airborne substances: the new revision of European Standard EN 689 Trevor Ogden UK and BOHS representative on the CEN Working Group

2 Elements of controlling exposure to airborne substances: 1. Principles of occupational hygiene* - COSHH Reg 7 (3), (4), (5) & Schedule 2A 2. Seek continual improvement - John Cherrie 3. Do not allow an OEL to be exceeded* - COSHH Reg 7(7b) *reflecting the Chemical Agents and the Carcinogens Directives

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4 European Law: Chemical Agents Directive: as soon as the limit is exceeded, the employer shall immediately take steps Carcinogens Directive: Exposure shall not exceed the limit value Exposure averaged over the reference period of the exposure limit must not be exceeded. An enforcer just needs one valid result >OEL to show that the law is broken If an employer gets a result <OEL, it only shows that the OEL is complied with at the time and place that the measurement is made.

5 How many measurements does an employer have to make, and how far below the OEL do they have to be, to be confident that at least 95% of exposures are < OEL?

6 Number of sources Background concentration Strength of sources Exposure Work-rate Work Habits Local exhaust ventilation rate General ventilation Exposure level results from the interplay of many factors

7 The problem: A typical exposure distribution: Personal exposure measurements of lead in air.* Measurement result (µg/m 3 ) Most exposures will be in this region but sometimes exposures are much higher *Data from Cope et al; see Rappaport and Kupper, 2008, Quantitative Exposure Assessment, ISBN

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9 Must be conducted by an appraiser, a person who is sufficiently trained and experienced in occupational hygiene principles, working and measurement techniques, to conduct the part of the assessment he or she is performing according to the state of the art Work with similarly Exposed Groups (SEGs) Test compliance

10 Test compliance: 1. Preliminary test with 3-5 measurements To quickly identify SEGs that clearly comply 2. Statistical test Fuller test requiring more measurements

11 Preliminary test Make three measurements from SEG If all results < 0.1 x OELV Or make four measurements If all < 0.15 x OELV Or make five measurements If all < 0.2 x OELV Then conclude: Compliance Based on computer simulations of lognormal distributions by INRS If any results at this or any other stage > OELV then conclude Non-compliance The preliminary test is in the text of the standard

12 If no decision can be reached with the Preliminary Test: Statistical test If all results are < OELV but the screening test is not met, then The appraiser shall select a statistical test of whether the exposures of the SEG comply with the OELV. The test shall measure, with at least 70 % confidence, whether less than 5 % of exposures in the SEG exceed the OELV. If any results at this or any other stage > OELV then conclude Non-compliance This specification is in the Standard; an EXAMPLE of a suitable test is in an Annex

13 Example of statistical test (Annex F) Calculate Geometric Mean and Geometric Standard Deviation and U R

14 Compare U R as calculated with a critical value U T from a table If U R > U T then, decision is Compliance

15 Frequency of exposure x lognormal distribution fitted to results Geometric Mean GM GM x GSD U R OELV Exposure x Annex F tests whether GM x GSD U R < OELV

16 A standard is authoritative advice. It does not have legal status unless there is a regulation requiring its use HSE COSHH Essentials Guidance G409. Exposure Measurement: Air Sampling If the results for a given task are below one third of the exposure limit, your controls are probably good enough. This is probably OK if you have at least 4 measurements in a SEG, but to reach a similar standard of proof to the preliminary test you would need 12 measurements.

17 Justification for preliminary test: GRZEBYK M., SANDINO J.P. Aspects statistiques et rôle de l'incertitude de mesurage dans l'évaluation de l'exposition professionnelle aux agents chimiques. INRS, ND 2231, Revue Hygiène et sécurité du travail, 09/ Justification of the compliance test used in Annex F: OGDEN T.L., LAVOUÉ J. Testing Compliance with Occupational Exposure Limits: Development of the British-Dutch Guidance J Occ Env Hyg 9:D63-D70 (2012) Summary of the standard: OGDEN T.L. The revised European Standard EN689: Testing compliance with exposure limits. Exposure 2017 issue 4, pp pational_exposure_limits_-_2017_revision_of_en_689.pdf (or go to Academia.edu and search for Trevor Ogden)